N-phosphonomethylglycine, otherwise known as glyphosate, is well known in the art as an effective post-emergent foliar applied herbicide. Glyphosate is an organic compound with three acidic groups, and in its acid form is relatively insoluble in water. Glyphosate is, therefore, normally formulated and applied as a water-soluble salt. Although monobasic, dibasic and tribasic salts of glyphosate can be made, it has generally been preferred to formulate and apply glyphosate, in the form of a monobasic salt, for example as a mono-isopropylamine, mono-potassium or mono-ammonium salt, or a dibasic salt such as the diammonium salt. Glyphosate herbicidal formulations are known which effectively comprise a mixture of mono-ammonium and di-ammonium salt, i.e., where the molar ratio of ammonium ion to glyphosate anion in the formulation is between 1 and 2.
When the terms “ammonium”, “monoammonium” and “diammonium” are used herein to refer to salts of glyphosate, these terms apply strictly to inorganic ammonium, i.e., NH4+, unless the context demands otherwise. Glyphosate rates and concentrations given herein, even where the glyphosate is present as a salt or salts, are expressed as acid equivalent (a.e.) unless the context demands otherwise.
For many applications, glyphosate salts require the presence of a suitable surfactant for best herbicidal performance. The surfactant can be provided either in the form of a concentrate, or it can be added by the end-user to the diluted spray solution. The choice of surfactant can be important since there are wide variations among surfactants in their ability to enhance the herbicidal efficacy of glyphosate for particular applications.
Use of a highly concentrated aqueous formulation of glyphosate in the form of a salt made with the inorganic base ammonia and potassium is advantageous. Ammonia and potassium are readily available, low in molecular weights, and relatively soluble in water. Additionally, they are natural nutrients for the growth of plants and other organisms. The use of ammonium and potassium salts of glyphosate for preparing aqueous concentrate formulations of glyphosate suitable for killing and controlling weeds and other plants has, however, been somewhat limited due to difficulties arising from chemical and physical properties of the ammonium and potassium salts of glyphosate, lack of suitable surfactants for preparing high-loaded liquid concentrates of such salts, reduced weed control, and requirement for complex processes for preparing liquid ammonium and potassium glyphosate compositions.
Accordingly, it is desirable to develop an aqueous glyphosate formulation (i) having high glyphosate a.e. loading, (ii) containing a suitable herbicidal efficacy enhancing surfactant that can be used for all salts of glyphosate, and (iii) having a optimized concentration at very low loading level of that surfactant to provide herbicidal effectiveness greater than that of commercial standard glyphosate salt formulations.
It is, therefore, an objective of the present invention to provide a storage-stable, highly concentrated aqueous formulation containing glyphosate together one or more agriculturally acceptable surfactants that enhance the herbicidal effectiveness of applications of the formulation.
It is a further objective of the present invention to provide a storage-stable, highly concentrated aqueous formulation containing glyphosate and one or more surfactants and having a superior level of herbicidal effectiveness by comparison with current commercial standard glyphosate salt formulations.
There is a particular need in the art for stable aqueous liquid formulations comprising a quaternary ammonium salt surfactant such as, e.g., a dialkoxylated dialkylammonium halide, and in particular for formulations comprising ammonium glyphosate and a dialkoxylated dialkylammonium salt surfactant. Such formulations are known to the art, but have generally required a significant fraction of a nonionic surfactant to maintain stability of the formulation. Additionally, the quaternary ammonium salt in many such formulations comprise the di(hydroxyethyl)methyl cocoamine, which is a highly effective